子線程搞事情,主線程來顯示

我們都知道把UI相關(guān)的事情放在主線程,但是如果當(dāng)我們要下載一張比較大的圖片來顯示的話,勢(shì)必會(huì)是一個(gè)耗時(shí)的操作,如果將其放在主線程操作,那么必然會(huì)對(duì)主線程造成阻塞,那么我們就需要將它放在子線程中去搞,搞完了再到主線程中去顯示UI.這也是我們最常使用GCD的地方了

dispatch_async(dispatch_get_global_queue(0, 0), ^{
        NSLog(@"我在子線程!開始我的耗時(shí)操作吧,我是不會(huì)阻塞主線程的");
        dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"事情搞完了回到主線程做事吧");
        });
    });

隊(duì)列幫你搞事情

串行隊(duì)列

接下來假設(shè)一個(gè)場(chǎng)景,在一個(gè)詳情頁中,需要先請(qǐng)求到詳情數(shù)據(jù),再通過詳情數(shù)據(jù)中的某個(gè)參數(shù)去請(qǐng)求評(píng)論列表,哇!是不是有點(diǎn)炸~
這個(gè)時(shí)候我們是不是想做一件事情,先去搞詳情數(shù)據(jù),等詳情數(shù)據(jù)搞到手了,再去搞評(píng)論列表的數(shù)據(jù).于是,我們這里可以搞一個(gè)串行隊(duì)列幫我們.因?yàn)闆]有真實(shí)數(shù)據(jù),所以用圖片下載代替說明一下串行隊(duì)列.

//圖片數(shù)據(jù)
static NSString * const picUrlOne = @"http://b.hiphotos.baidu.com/image/pic/item/0823dd54564e925838c205c89982d158ccbf4e26.jpg";
static NSString * const picUrlTwo = @"http://e.hiphotos.baidu.com/image/pic/item/d1160924ab18972bf05282ece3cd7b899e510aaf.jpg";
static NSString * const picUrlThree = @"http://c.hiphotos.baidu.com/image/pic/item/58ee3d6d55fbb2fb3943da344a4a20a44623dca8.jpg";
static NSString * const picUrlFour = @"http://e.hiphotos.baidu.com/image/pic/item/1ad5ad6eddc451da9dd88ecdb3fd5266d01632ed.jpg";

- (void)loadImagesBySerial
{
    //step one:創(chuàng)建一個(gè)串行隊(duì)列
    dispatch_queue_t serialQueue = dispatch_queue_create("dispatch.serial", DISPATCH_QUEUE_SERIAL);
    //step two:講我們要做的事情分別加入到隊(duì)列里面
    [self loadImageByDispatch:serialQueue threadcomplete:^{
        NSLog(@"image1StartDownLoad");
        _imageData1 = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:picUrlOne]]];
    } complete:^{
        _imageOne.image = _imageData1;
        NSLog(@"image1DownLoadOver");
    }];
    
    [self loadImageByDispatch:serialQueue threadcomplete:^{
        NSLog(@"image2StartDownLoad");
        _imageData2 = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:picUrlTwo]]];
    } complete:^{
        _imageTwo.image = _imageData2;
        NSLog(@"image2DownLoadOver");
    }];
    
    [self loadImageByDispatch:serialQueue threadcomplete:^{
        NSLog(@"image3StartDownLoad");
        //故意搞一個(gè)延遲,證明當(dāng)遇到耗時(shí)的情況,任務(wù)4會(huì)等到任務(wù)3完成才執(zhí)行
        [NSThread sleepForTimeInterval:3];
        _imageData3 = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:picUrlThree]]];
    } complete:^{
        _imageThree.image = _imageData1;
        NSLog(@"image3DownLoadOver");
    }];
    
    [self loadImageByDispatch:serialQueue threadcomplete:^{
        NSLog(@"image4StartDownLoad");
        _imageData4 = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:picUrlFour]]];
        //step three:任務(wù)至此,所有耗時(shí)操作都已在子線程完成
    } complete:^{
        _imageFour.image = _imageData1;
        NSLog(@"image4DownLoadOver");
        //step four:當(dāng)我們最后一個(gè)任務(wù)完成,即可在主線程搞事情了~我們甚至可以將所有的圖片顯示放在這個(gè)位置,讓他們一起顯示出來
        /*
        _imageOne.image = _imageData1;
            _imageTwo.image = _imageData2;
            _imageThree.image = _imageData3;
            _imageFour.image = _imageData4;
        */
    }];
}

- (void)loadImageByDispatch:(dispatch_queue_t)queue threadcomplete:(void(^)())threadComplete complete:(void(^)())complete
{
    dispatch_async(queue, ^{
        if (threadComplete) {
            threadComplete();
        }
        dispatch_async(dispatch_get_main_queue(), ^{
            if (complete) {
                complete();
            }
        });
    });
}

并行隊(duì)列

再來搞個(gè)事兒,比如:我們現(xiàn)在有一大堆數(shù)據(jù)要處理,顯然是耗時(shí)的,不能去阻塞主線程吧~那好,現(xiàn)在子線程你得幫我搞事情,那么問題來了,我需要在頁面顯示來自4個(gè)不同模塊的數(shù)據(jù),且這些數(shù)據(jù)處理都是耗時(shí)的,那么并行隊(duì)列就可以出來搞搞事情了,還是用上面下載圖片的例子來說明一下并行隊(duì)列

- (void)loadImagesByConcurrent
{
    //step one:創(chuàng)建一個(gè)并行隊(duì)列
    dispatch_queue_t concurrentQueue = dispatch_queue_create("dispatch_concurrent", DISPATCH_QUEUE_CONCURRENT);
    //step two:開始我們要執(zhí)行的4個(gè)任務(wù)
    [self loadImageByDispatch:concurrentQueue threadcomplete:^{
        NSLog(@"image1StartDownLoad");
        _imageData1 = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:picUrlOne]]];
    } complete:^{
        _imageOne.image = _imageData1;
        NSLog(@"image1DownLoadOver");
    }];
    
    [self loadImageByDispatch:concurrentQueue threadcomplete:^{
        NSLog(@"image2StartDownLoad");
        _imageData2 = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:picUrlTwo]]];
    } complete:^{
        _imageTwo.image = _imageData2;
        NSLog(@"image2DownLoadOver");
    }];
    
    [self loadImageByDispatch:concurrentQueue threadcomplete:^{
        NSLog(@"image3StartDownLoad");
        [NSThread sleepForTimeInterval:3];
        _imageData3 = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:picUrlThree]]];
    } complete:^{
        _imageThree.image = _imageData1;
        NSLog(@"image3DownLoadOver");
    }];
    
    [self loadImageByDispatch:concurrentQueue threadcomplete:^{
        NSLog(@"image4StartDownLoad");
        _imageData4 = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:picUrlFour]]];
    } complete:^{
        _imageFour.image = _imageData1;
        NSLog(@"image4DownLoadOver");
    }];
}

至此,你會(huì)發(fā)現(xiàn)我們的4個(gè)任務(wù)是幾乎同時(shí)開始的,至于期間某個(gè)任務(wù)有阻塞,我們管不了,最終的哪個(gè)先結(jié)束我們也不知道_{所以我們看到的結(jié)果也是分別顯示的}這就有點(diǎn)意思了,如果我們需要拿到所有結(jié)果一起來顯示,又該咋辦呢~~_{這個(gè)時(shí)候我們就需要dispatch_group這個(gè)東西幫忙了}
還是上面下載圖片的例子~

- (void)groupEnterAndLeave
{
    //step one:創(chuàng)建一個(gè)并行隊(duì)列
    dispatch_queue_t concurrentQueue = dispatch_queue_create("dispatch.concurrent", DISPATCH_QUEUE_CONCURRENT);
    //step two:再來一個(gè)組
    dispatch_group_t concurrentGroup = dispatch_group_create();
    
    /**
    dispatch_group_enter,dispatch_group_leave成對(duì)出現(xiàn)~~~
    */
    dispatch_group_enter(concurrentGroup);
    [self loadImageByDispatch:concurrentQueue threadcomplete:^{
        _imageData1 = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:picUrlOne]]];
        dispatch_group_leave(concurrentGroup);
    } complete:^{
        
    }];
    
    dispatch_group_enter(concurrentGroup);
    [self loadImageByDispatch:concurrentQueue threadcomplete:^{
        _imageData2 = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:picUrlTwo]]];
        dispatch_group_leave(concurrentGroup);
    } complete:^{
        
    }];
    
    dispatch_group_enter(concurrentGroup);
    [self loadImageByDispatch:concurrentQueue threadcomplete:^{
        _imageData3 = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:picUrlThree]]];
        dispatch_group_leave(concurrentGroup);
    } complete:^{
        
    }];
    
    dispatch_group_enter(concurrentGroup);
    [self loadImageByDispatch:concurrentQueue threadcomplete:^{
        _imageData4 = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:picUrlFour]]];
        dispatch_group_leave(concurrentGroup);
    } complete:^{
        
    }];
    //step three:所有任務(wù)完成,收到通知~
    dispatch_group_notify(concurrentGroup, concurrentQueue, ^{
        NSLog(@"AllTaskOver");
        dispatch_async(dispatch_get_main_queue(), ^{
            _imageOne.image = _imageData1;
            _imageTwo.image = _imageData2;
            _imageThree.image = _imageData3;
            _imageFour.image = _imageData4;
        });
    });
}

除了單例,還能這樣玩

比如只希望在整個(gè)工程的生命周期內(nèi),只執(zhí)行一次某段代碼,可以這樣玩兒

static dispatch_once_t once;
    dispatch_once(&once, ^{
       /**
       這里是只想執(zhí)行一次的代碼
       */
    });

延時(shí)執(zhí)行

/**
第一個(gè)參數(shù)表示延時(shí)時(shí)間,第二個(gè)參數(shù)是在哪個(gè)隊(duì)列執(zhí)行
*/
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(5 * NSEC_PER_SEC)),dispatch_get_main_queue(), ^{
        //需要做的延時(shí)操作
    });

零零星星寫了一些,還有很多沒有寫,具體在實(shí)戰(zhàn)中遇到的坑之后再寫,暫時(shí)就這樣.